This invention relates antennas and in particular to antennas having individual elements that are designed to scatter an incident field with proper phase.
With an increasing demand in recent years for worldwide communication systems such as telephone, TV transmission, Internet, to mention a few, the demand for satellite communication is increasing accordingly. Recently, new satellite communication technologies have been developed for multimedia applications. Due to its compact nature the microstrip patch is widely used as the radiating element in reflectarray systems.
A microstrip reflectarray antenna is a low profile structure that comprises a thin, flat conducting backed substrate on which a lattice of patch radiators is etched. A feed antenna illuminates the array of individual elements that are designed to scatter the incident field with the proper phase required to realize a uniform phase front on the antenna aperture. Several different versions of the printed reflectarray structures have been developed and reported previously such as, variable length patches disclosed in: D. M. Pozar, T. A. Metzler, xe2x80x9cAnalysis of a reflectarray antenna using microstrip patches of variable sizexe2x80x9d, Elect. Letters, Vol.29, April 1993, pp. 657-659, variable stub loaded patches in U.S. Pat. No. 4,684,952 issued to R. W. Munson, August 1987, and variable patch rotation angle in: J. Huang, R. J. Pogorzelski, xe2x80x9cA Ka-band Microstrip Reflectarray with Elements Having Variable Rotation Angles,xe2x80x9d IEEE Trans. Of Antennas Propagat., Vol. 46, No. 5, May 1998 pp 650-656, which are incorporated hereby for reference.
The bandwidth of the reflectarray antenna is limited by phase errors as the signal frequency is shifted away from the design frequency of the antenna.
It is an object of the invention to complement the prior art by providing an antenna where the required phase shift at each position on the antenna surface is obtained by varying the inductive load of the patches using the slots of varying length sizes beneath the patches.
It is further an object of the invention to provide an antenna where the inductive load of the patches is optically controlled.
The reflectarray antenna according to the invention comprises a dielectric substrate layer disposed on a ground plane. An array of micro-strip patches of similar size are arranged on the top surface of the substrate layer. A periodic configuration of slots of variable size is provided at the bottom surface of the substrate layer. A required phase shift at each position on the reflectarray surface is obtained by adjusting the slot length on the ground plane. The incident wave from the feed excites the dominant mode on the microstrip patches. When there is no slot on the ground plane, each patch radiates the energy at its resonant frequency. The presence of slots acts as an inductive loading of the patches, which introduces a phase shift in the patch response. The inductance of each slot depends on its length. In accordance with an aspect of the invention the phase shift of the individual micro-strips is modified by shining an appropriate optical image onto each individual element which generates plasma in the exposed regions, thereby altering the radiation characteristics of the reflectarray. This approach is highly advantageous for dynamic beam scanning and beam shaping.
In accordance with the present invention there is provided an antenna comprising:
a dielectric substrate layer having a top surface and a bottom surface, the top surface for providing a radiating array that is other than slot fed;
an array of radiating elements in contact with the top surface forming the radiating array, the radiating elements for radiating one of an emitted and reflected electromagnetic signal; and,
a bottom surface layer attached to the bottom surface of the dielectric substrate layer, the bottom surface layer having an array of openings, the openings having a variable dimension for providing a variable inductive loading acting on the radiating elements in order to induce a predetermined phase shift in the radiated electromagnetic signal.
In accordance with the present invention there is further provided an antenna comprising:
a dielectric substrate layer having a top surface and a bottom surface, the top surface for providing a radiating array that is other than slot;
an array of radiating elements in contact with the top surface forming the radiating array, the radiating elements for radiating one of an emitted and reflected electromagnetic signal;
a bottom surface layer attached to the bottom surface of the dielectric substrate layer, the bottom surface layer having an array of openings, the openings having a variable dimension for providing a variable inductive loading acting on the radiating elements in order to induce a predetermined phase shift in the radiated electromagnetic signal; and,
a semiconductor substrate layer interposed between the dielectric substrate layer and the bottom surface layer, the semiconductor substrate layer for providing a variable inductive loading acting on the radiating elements through photo-induced plasma effect generated by illumination through the openings of a mask which is set between the optical source and the semiconductor.
In accordance with an aspect of the present invention there is provided a method for controlling a phase shift of an incoming electromagnetic signal in an antenna comprising the steps of:
providing a dielectric substrate layer having a top surface and a bottom surface, the top surface for providing a radiating array that is other than slot;
providing an array of radiating elements in contact with the top surface forming the radiating array, the radiating elements for radiating one of an emitted and reflected electromagnetic signal;
providing a bottom surface layer attached to the bottom surface of the dielectric substrate layer, the bottom surface layer having an array of openings, the openings having a variable dimension for providing a variable inductive loading acting on the radiating elements in order to induce a predetermined phase shift in the radiated electromagnetic signal; and,
adjusting the phase shift of the electromagnetic signal by adjusting the phase shift of the radiating elements by varying the dimension of the openings.
In accordance with the aspect of the present invention there is further provided a method for controlling a phase shift in a reflectarray antenna comprising the steps of:
providing a dielectric substrate layer having a top surface and a bottom surface, the top surface for providing a radiating array that is other than slot;
providing an array of radiating elements in contact with the top surface forming the radiating array, the radiating elements for radiating one of an emitted and reflected electromagnetic signal;
providing a bottom surface layer attached to the bottom surface of the dielectric substrate layer, the bottom surface layer having an array of openings, the openings having a variable dimension for providing a variable inductive loading acting on the radiating elements in order to induce a predetermined phase shift in the radiated electromagnetic signal;
providing a semiconductor substrate layer interposed between the dielectric substrate layer and the bottom surface layer, the semiconductor substrate layer for providing a variable inductive loading acting on the radiating elements through photoinduced plasma effect; and,
adjusting the phase shift of the radiating elements by illuminating with a predetermined optical intensity the semiconductor substrate through the openings for controllably generating the photo-induced plasma effect.